Sole Structure

ABSTRACT

A sole structure includes an upper midsole made of an elastic material and a lower midsole made of an elastic material and bonded from below to the upper midsole. The upper midsole has first protrusions protruding toward the lower midsole, and the tip ends of the first protrusions are in contact with the lower midsole such that the tip ends of the first protrusions can move with respect to the lower midsole.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to Japanese Patent Application No. 2018-177278 filed on Sep. 21, 2018, the entire disclosure of which is incorporated by reference herein.

BACKGROUND

The present disclosure relates to sole structures for shoes which include an upper midsole made of an elastic material and a lower midsole made of an elastic material and bonded from below to the upper midsole.

Japanese Patent No. 4465040 discloses a sole structure for shoes which includes an upper midsole made of an elastic material and a lower midsole made of an elastic material and bonded from below to the upper midsole. In this sole structure, the upper midsole has protrusions protruding toward the lower midsole, and the tip ends of the protrusions are in close contact with the lower midsole, so that the load of a wearer is dispersed to the lower midsole through the protrusions.

SUMMARY

In Japanese Patent No. 4465040, the tip ends of the protrusions of the upper midsole are in close contact with the lower midsole. Accordingly, when the wearer's foot lands, the protrusions of the upper midsole are pressed against the lower midsole by the load of the wearer. At this time, the protrusions are compressively deformed in the direction in which the protrusions are pressed, but the tip ends of the protrusions do not move with respect to the lower midsole in a direction along the upper surface of the lower midsole. Impact energy therefore will not be sufficiently absorbed, increasing the burden on the wearer's foot.

The present disclosure was developed in view of the above circumferences and it is an object of the present disclosure to reduce the burden that is placed on a wearer's foot upon landing.

In order to achieve the above object, a first aspect of the present disclosure is a sole structure for a shoe including: an upper midsole made of an elastic material; and a lower midsole made of an elastic material and bonded from below to the upper midsole. At least one of the upper midsole and the lower midsole has a protrusion protruding toward the other midsole, and when a shoe is in an unworn state, a tip end of the protrusion is not in contact with the other midsole or is in contact with the other midsole such that the tip end of the protrusion can move with respect to the other midsole, and when a foot lands, the tip end of the protrusion is pressed against the other midsole and is thus moved with respect to the other midsole in a direction along a surface of the other midsole.

In the first aspect, when the upper midsole is pressed against the lower midsole by the load of a wearer upon landing, the protrusion is flexurally deformed with its tip end being moved with respect to the other midsole in a direction along a surface of the other midsole. At this time, the protrusion is also compressively deformed in the direction in which the protrusion is pressed against the other midsole. Accordingly, impact energy is more efficiently absorbed and the burden on the wearer's foot is reduced, as compared to the configuration of Japanese Patent No. 4465040 in which the protrusions cannot be flexurally deformed.

According to a second aspect of the present disclosure, in the first aspect, the protrusion is tapered so that its tip end is thinner than its base end.

In the second aspect, since the protrusion is thinner at its tip end and gradually becomes thicker toward its base end, the protrusion is less easily compressively deformed at its base end than at its tip end. Accordingly, upon landing, the upper midsole is at first quickly moved downward toward the lower midsole, but the movement of the upper midsole toward the lower midsole gradually slows down. This gives a good feel.

According to a third aspect of the present disclosure, in the first aspect, a plurality of the protrusions are formed, and the protrusions adjacent to each other in a longitudinal direction are spaced apart from each other in the longitudinal direction.

In the third aspect, flexural deformation of each protrusion in the longitudinal direction is less likely to be hindered by its adjacent protrusions when the wearer walks or runs while shifting the load in the longitudinal direction, as compared to the case where there is no spacing between the protrusions adjacent to each other in the longitudinal direction. Accordingly, the burden on the wearer's foot is more reliably reduced.

According to a fourth aspect of the present disclosure, in the first aspect, the protrusion is formed in a region supporting a wearer's heel.

In the fourth aspect, when the wearer walks or runs with a heel landing, the protrusion is more reliably pressed against the other midsole by the load of the wearer upon landing. Accordingly, the burden on the wearer's foot is more reliably reduced.

According to a fifth aspect of the present disclosure, in the first aspect, a longitudinal dimension of the protrusion is smaller than a lateral dimension thereof.

In the fifth aspect, the protrusion tends to be bent in the longitudinal direction. Accordingly, the protrusion is more reliably flexurally deformed upon landing, and the burden on the wearer's foot is more reliably reduced.

A sixth aspect of the present disclosure is a sole structure for a shoe including: an upper midsole made of an elastic material; and a lower midsole made of an elastic material and bonded to, or formed integrally with, a lower surface of the upper midsole. At least one of the upper midsole and the lower midsole has a protrusion protruding toward the other midsole, the protrusion has a bent or narrowed intended deformation portion formed in its intermediate portion in a direction in which the protrusion protrudes, and a tip end of the protrusion is in close contact with, is bonded, or is formed integrally with, the other midsole.

In the sixth aspect, when the upper midsole is pressed against the lower midsole by the load of a wearer upon landing, the protrusion is flexurally deformed with its intended deformation portion being moved with respect to a surface of the other midsole in a direction along the surface of the other midsole. Accordingly, impact energy is more efficiently absorbed and the burden on the wearer's foot is reduced, as compared to the configuration of Japanese Patent No. 4465040 in which the protrusions cannot be flexurally deformed.

According to a seventh aspect of the present disclosure, in the sixth aspect, the intended deformation portion is bent or narrowed so as to be recessed rearward.

In the seventh aspect, the intended deformation portion is easily moved rearward with respect to the surface of the other midsole. Accordingly, when the wearer walks or runs while shifting the load in a longitudinal direction, the protrusion is more reliably flexurally deformed upon landing, and the burden on the wearer's foot is more reliably reduced.

The present disclosure can reduce the burden that is placed on a wearer's foot upon landing.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view of a sole structure according to a first embodiment of the present disclosure;

FIG. 2 is a side view of the sole structure as viewed from the lateral side;

FIG. 3 is a sectional view of an upper midsole taken along line III-III in FIG. 1;

FIG. 4 is a sectional view of the upper midsole taken along line IV-IV in FIG. 1;

FIG. 5 is a sectional view taken along line V-V in FIG. 1;

FIG. 6 is a sectional view taken along line VI-VI in FIG. 1;

FIG. 7 is a sectional view taken along line VII-VII in FIG. 1;

FIG. 8A is a front view of a first protrusion of a sole structure according to a second embodiment, FIG. 8B is a view corresponding to FIG. 8A, showing a modification of the second embodiment, and FIG. 8C is a view corresponding to FIG. 8A, showing another modification of the second embodiment; and

FIG. 9A is a front view of a first protrusion of a sole structure according to a modification of the first embodiment, FIG. 9B is a view corresponding to FIG. 9A, showing another modification of the first embodiment, FIG. 9C is a view corresponding to FIG. 9A, showing still another modification of the first embodiment, FIG. 9D is a view corresponding to FIG. 9A, showing yet another modification of the first embodiment, and FIG. 9E is a view corresponding to FIG. 9A, showing a further modification of the first embodiment.

DETAILED DESCRIPTION

Embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. The following description of the embodiments is merely illustrative in nature and is not intended to limit the invention, its application or uses.

First Embodiment

FIGS. 1 to 7 show a sole structure 1 according to a first embodiment of the present disclosure for supporting the sole of a wearer's foot. For example, shoes having an upper (not shown) etc. on the sole structure 1 are used as walking shoes, running shoes, shoes for indoor sports, shoes for ball games that are played on the ground or lawn, etc.

Although the sole structure 1 for left shoes will be described below, right shoes can be configured symmetrically with left shoes.

In the following description, the terms “upper (upper side)” and “lower (lower side)” indicate the vertical positional relationship in the sole structure 1, and the terms “front (front side)” and “rear (rear side)” indicate the longitudinal positional relationship in the sole structure 1.

The sole structure 1 includes an upper midsole 3 that supports the entire sole of a foot. An outer peripheral region of the upper surface of the lower midsole 5 is bonded to an outer peripheral region of the lower surface of the upper midsole 3. An outsole 7 is bonded from below to the lower surface of the lower midsole 5. The upper midsole 3 and the lower midsole 5 are made of a soft elastic material. Examples of suitable materials for the upper midsole 3 and the lower midsole 5 include thermoplastic synthetic resins such as ethylene-vinyl acetate copolymer (EVA) and their foams, thermosetting resins such as polyurethane (PU) and their foams, and rubber materials such as butadiene rubber and chloroprene rubber and their foams. The outsole 7 is made of an elastic material harder than the elastic material forming the upper midsole 3 and the lower midsole 5. Examples of suitable materials for the outsole 7 include thermoplastic resins such as ethylene-vinyl acetate copolymer (EVA), thermosetting resins such as polyurethane (PU), and rubber materials such as butadiene rubber and chloroprene rubber.

Of a bonded region of the lower surface of the upper midsole 3 which is bonded to the lower midsole 5, a region corresponding to the arch of the wearer's foot in the longitudinal direction forms a protruding region R1 that convexly protrudes toward the lateral side in the middle in the longitudinal direction. Of a non-bonded region of the lower surface of the upper midsole 3 which is not bonded to the lower midsole 5, a region corresponding to the arch of the wearer's foot in the longitudinal direction forms a narrow region R2 that gradually narrows from its both longitudinal ends so as to have the smallest width in the middle in the longitudinal direction.

The upper midsole 3 has a main surface portion 3 a that forms the upper surface of the upper midsole 3. The right and left ends of the main surface portion 3 a curve upward towards the right and left. The main surface portion 3 a except for its right and left ends is substantially flat. A first protruding portion 3 b extending in the longitudinal direction is integrally formed on a part of a non-bonded region R3 of the lower surface of the main surface portion 3 a which is not bonded to the lower midsole 5, namely on a region supporting the wearer's heel and midfoot and the lateral side of the wearer's forefoot. However, the first protruding portion 3 b is not formed on the outer peripheral end of the region supporting the wearer's heel and midfoot and the lateral side of the wearer's forefoot. The height H1 of the first protruding portion 3 b (see FIG. 3) gradually decreases from the rear to the front so that the height H1 is the smallest at the front. A plurality of mountain-like first protrusions 3 c protruding toward the lower midsole 5 are formed integrally on a part of the end face of the first protruding portion 3 b, namely on an entire region supporting the wearer's heel and midfoot. The entire surface of each of the first protrusions 3 c is curved. A load path line LP in FIG. 1 represents the direction in which the load is expected to be shifted when the shoe lands. The first protrusions 3 c adjacent to each other in the direction along the load path line LP are located at intervals D of approximately 1 mm in the direction along the load path line LP. The load path line LP of the present embodiment extends in the longitudinal direction with slight curves. Accordingly, the first protrusions 3 c adjacent to each other in the longitudinal direction are spaced apart from each other in the longitudinal direction. The first protrusions 3 c have an elliptical shape that is longer in a direction crossing the load path line LP as viewed in the direction in which the first protrusions 3 c protrude. The longitudinal dimension W1 of the first protrusions 3 c is smaller than the lateral dimension W2 thereof. A plurality of mountain-like second protrusions 3 d protruding toward the lower midsole 5 are formed integrally on a part of the end face of the first protruding portion 3 b where the first protrusions 3 c are not formed, namely on an entire region supporting the wearer's forefoot. The entire surface of each of the second protrusions 3 d is curved. The second protrusions 3 d adjacent to each other in the longitudinal direction contact each other. Most of the second protrusions 3 d have a generally true circular shape as viewed in the direction in which the second protrusions 3 d protrude. The height HT2 of the second protrusions 3 d is made smaller than the height HT1 of the first protrusions 3 c. Specifically, the height HT1 of the first protrusions 3 c is 5 to 6 mm, and the height HT2 of the second protrusions 3 d is 2 to 3 mm. A second protruding portion 3 e protruding downward is integrally formed on a part of the non-bonded region R3 of the lower surface of the main surface portion 3 a, namely on a region supporting the medial side (ball) of the wearer's forefoot. The second protruding portion 3 e is spaced apart from the first protruding portion 3 b in the lateral direction. A plurality of third protrusions 3 f protruding toward the lower midsole 5 are integrally formed on the entire end face of the second protruding portion 3 e. Most of the third protrusions 3 f have a generally true circular shape as viewed in the direction in which the third protrusions 3 f protrude. The height HT3 of the third protrusions 3 f is made smaller than the height HT1 of the first protrusions 3 c. The average size (area) of the third protrusions 3 f as viewed in the direction in which the third protrusions 3 f protrude is made larger than the average size (area) of the first protrusions 3 c and the average size (area) of the second protrusions 3 d as viewed in the direction in which the first and second protrusions 3 c, 3 d protrude. The tip ends of the third protrusions 3 f have a flat top surface.

A recessed portion 5 a is formed in the entire upper surface of the lower midsole 5 except for its outer peripheral region, namely in a region of the upper surface of the lower midsole 5 which is not bonded to the upper midsole 3. A long hole 5 b is formed at a position behind the middle in the longitudinal direction of the bottom surface of the recessed portion 5 a. The long hole 5 b extends through the bottom of the recessed portion 5 a. The long hole 5 b extends in the longitudinal direction, and the longitudinal length of the long hole 5 b is about ⅓ of the overall longitudinal length of the lower midsole 5.

The first protruding portion 3 b and the second protruding portion 3 e of the upper midsole 3 are accommodated in the recessed portion 5 a of the lower midsole 5. The tip ends of the first protrusions 3 c of the upper midsole 3 are in contact with the bottom surface of the recessed portion 5 a of the lower midsole 5 when the shoe with the sole structure 1 is not worn (unworn state). The tip ends of the first protrusions 3 c are in contact with, but are not in close contact with, the bottom surface of the recessed portion 5 a of the lower midsole 5. The tip ends of the first protrusions 3 c can therefore move relative to the bottom surface of the recessed portion 5 a of the lower midsole 5 in a direction along the bottom surface of the recessed portion 5 a. On the other hand, the tip ends of the second and third protrusions 3 d, 3 f of the upper midsole 3 are separated from the bottom surface of the recessed portion 5 a of the lower midsole 5.

When the wearer of shoes having such a sole structure 1 walks or runs while shifting the load in the longitudinal direction and his/her heel lands first, the upper midsole 3 is pressed against the lower midsole 5 by the load. At this time, the tip ends of the first protrusions 3 c of the upper midsole 3 are pressed against the lower midsole 5. The first protrusions 3 c of the upper midsole 3 are thus flexurally deformed with their tip ends being moved rearward with respect to the upper surface of the lower midsole 5. At the same time, the first protrusions 3 c of the upper midsole 3 are also compressively deformed in the direction in which the first protrusions 3 c are pressed against the lower midsole 5. Accordingly, the impact energy is more efficiently absorbed and the burden on the wearer's foot is reduced, as compared to the configuration of Japanese Patent No. 4465040 in which the protrusions cannot be flexurally deformed. Since the first protrusions 3 c are thinner at their tip ends and gradually become thicker toward their base ends, the first protrusions 3 c are less easily compressively deformed at their base ends than at their tip ends. Accordingly, upon landing, the upper midsole 3 is at first quickly moved downward toward the lower midsole 5, but the movement of the upper midsole 3 toward the lower midsole 5 gradually slows down. This gives a good feel. Moreover, flexural deformation of each of the first protrusions 3 c in the longitudinal direction is less likely to be hindered by its adjacent first protrusions 3 c, as compared to the case where there is no spacing between the first protrusions 3 c adjacent to each other in the longitudinal direction. Accordingly, the burden on the wearer's foot is more reliably reduced. Furthermore, since the longitudinal dimension W1 of the first protrusions 3 c is smaller than the lateral dimension W2 thereof, the first protrusions 3 c tends to be bent in the longitudinal direction. Accordingly, the first protrusions 3 c are more reliably flexurally deformed upon landing, and the burden on the wearer's foot is more reliably reduced.

When the wearer strikes the ground with his/her forefoot after heel landing, the tip ends of the second protrusions 3 d of the upper midsole 3 are pressed against the lower midsole 5, and the striking force is transferred from the upper midsole 3 to the ground through the lower midsole 5 and the outsole 7. The height HT2 of the second protrusions 3 d and the height HT3 of the third protrusions 3 f are smaller than the height HT1 of the first protrusions 3 c, and when the shoe is in the unworn state, the tip ends of the second and third protrusions 3 d, 3 f are separated from the bottom surface of the recessed portion 5 a of the lower midsole 5. The second and third protrusions 3 d, 3 f are therefore less compressed in the direction in which the second and third protrusions 3 d, 3 f protrude than in the case where the sole structure 1 is configured so that the second and third protrusions 3 d, 3 f have the same height HT1 as the first protrusions 3 c and the tip ends of the second and third protrusions 3 d, 3 f are in contact with the bottom surface of the recessed portion 5 a of the lower midsole 5 when the shoe is in the unworn state. Energy loss due to compressive deformation of the second and third protrusions 3 d, 3 f is thus reduced, and the striking force is sufficiently transferred to the ground. The size (area) of the third protrusions 3 f as viewed in the direction in which the third protrusions 3 f protrude is larger than the size (area) of the first protrusions 3 c and the size (area) of the second protrusions 3 d as viewed in the direction in which the first and second protrusions 3 c, 3 d protrude. Accordingly, the striking force by the ball of the wearer's foot is more easily transferred to the ground as compared to the case where the third protrusions 3 f have about the same area as the first protrusions 3 c and the second protrusions 3 d as viewed in the direction in which the first, second, and third protrusions 3 c, 3 d, 3 f protrude. Moreover, since the tip ends of the third protrusions 3 f have a flat top surface, the striking force by the ball of the wearer's foot is more easily transferred to the ground as compared to the case where the third protrusions 3 f have a tapered tip end.

According to the first embodiment, the first protrusions 3 c have a rounded tip end and the tip ends of the first protrusions 3 c are in contact with the lower midsole 5 such that the tip ends of the first protrusions 3 c can move with respect to the lower midsole 5. Accordingly, the shoe with this sole structure 1 is less likely to make strange noise by friction between the tip ends of the first protrusions 3 c and the lower midsole 5 as compared to the case where the tip ends of the first protrusions 3 c have a flat top surface and are in close contact with the lower midsole 5 such that the tip ends of the first protrusions 3 c cannot move with respect to the lower midsole 5.

Second Embodiment

FIG. 8A shows a first protrusion 3 c of a sole structure 1 according to a second embodiment of the present disclosure. In the second embodiment, the first protrusion 3 c has a cylindrical shape and has an intended deformation portion 3 g formed in its intermediate portion in the direction in which the first protrusion 3 c protrudes. The intended deformation portion 3 g is bent with its apex pointing the opposite direction to the direction in which the load is expected to be shifted. In the second embodiment as well, the expected load path line LP extends in the longitudinal direction with slight curves. The intended deformation portion 3 g is therefore bent so as to be recessed rearward. Accordingly, the part of the first protrusion 3 c which is located on the tip end side of the intended deformation portion 3 g is tilted upward toward the rear, and the part of the first protrusion 3 c which is located on the base end side of the intended deformation portion 3 g is tilted upward toward the front. The tip end of the first protrusion 3 c has a flat top surface and is in close contact with the bottom surface of the recessed portion 5 a of the lower midsole 5.

Accordingly, when a wearer of shoes having the sole structure 1 of the second embodiment walks or runs while shifting the load in the longitudinal direction and his/her heel lands first, the upper midsole 3 is pressed against the lower midsole 5 by the load. At this time, the first protrusions 3 c are flexurally deformed with their intended deformation portions 3 g moved rearward with respect to the upper surface of the lower midsole 5. Accordingly, the impact energy is more efficiently absorbed and the burden on the wearer's foot is reduced as compared to the configuration of Japanese Patent No. 4465040 in which the protrusions cannot be flexurally deformed. Moreover, the intended deformation portions 3 g are easily moved rearward with respect to the upper surface of the lower midsole 5. Accordingly, the first protrusions 3 c are more reliably flexurally deformed upon landing, and the burden on the wearer's foot is more reliably reduced.

In the first and second embodiments, the upper midsole 3 has the first, second, and third protrusions 3 c, 3 d, 3 f that protrude toward the lower midsole 5. Alternatively, the lower midsole 5 may have first, second, and third protrusions that protrude toward the upper midsole 3.

In the first and second embodiments, the first protrusions 3 c are formed in the region supporting the heel and midfoot of the wearer's foot, and the second protrusions 3 d and the third protrusions 3 f are formed in the region supporting the forefoot of the wearer's foot. Alternatively, the second protrusions 3 d and the third protrusions 3 f may be formed in the region supporting the heel and midfoot of the wearer's foot, and the first protrusions 3 c may be formed in the region supporting the forefoot of the wearer's foot. This configuration reduces the burden that is placed on the wearer's foot upon landing when the wearer walks or runs with a forefoot landing (forefoot lands first and heel then strikes the ground). Moreover, the striking force by the heel is sufficiently transferred to the ground.

The first protrusions 3 c may be formed on the medial side and the second protrusions 3 d and the third protrusions 3 f may be formed on the lateral side of the first protrusions 3 c. This configuration reduces the burden that is placed on the wearer's foot upon landing when the wearer plays such a sport or ball game that the medial side of his/her foot lands first and the lateral side thereof then strikes the ground. Moreover, the striking force by the lateral side of the foot is sufficiently transferred to the ground. Alternatively, the first protrusions 3 c may be formed on the lateral side and the second protrusions 3 d and the third protrusions 3 f may be formed on the medial side of the first protrusions 3 c. This configuration reduces the burden that is placed on the wearer's foot upon landing when the wearer plays such a sport or ball game that the lateral side of his/her foot lands first and the medial side thereof then strikes the ground. Moreover, the striking force by the medial side of the foot is sufficiently transferred to the ground.

In the first embodiment, the first protrusion 3 c is a mountain-like protrusion whose entire surface is curved. As shown in FIGS. 9A to 9C, the first protrusion 3 c may have a generally conical shape with only its tip end surface being curved. As shown in FIG. 9B, the side surface of the first protrusion 3 c may be bent at an intermediate position in the direction in which the first protrusion 3 c protrudes such that the side surface of the first protrusion 3 c is steeper on the base end side than on the tip end side. As shown in FIG. 9D, the first protrusion 3 c may be formed by a plurality of hemispherical protrusions stacked on top of each other in descending order of diameter from the base end toward the tip end. As shown in FIG. 9E, the first protrusion 3 c may be formed by a plurality of circular plates stacked on top of each other in descending order of diameter from the base end toward the tip end.

In the first embodiment, the tip ends of the first protrusions 3 c are in contact with the upper surface of the midsole 5 when the shoe is in the unworn state. However, the tip ends of the first protrusions 3 c may not be in contact with the upper surface of the lower midsole 5 and thus may be separated from the lower midsole 5 when the shoe is in the unworn state as long as the shape, height, etc. of the first protrusions 3 c are determined so that the tip ends of the first protrusions 3 c will be pressed against the lower midsole 5 and will move with respect to the lower midsole 5 in the direction along the upper surface (front surface) of the lower midsole 5 when the wearer's foot lands.

In the second embodiment, the intended deformation portion 3 g is a portion that is bent so as to be recessed rearward. As shown in FIG. 8B, the intended deformation portion 3 g may be a narrowed part that is recessed rearward. As shown in FIG. 8C, the intended deformation portion 3 g may be a narrowed part that is recessed along the entire circumference.

In the second embodiment, the tip ends of the first protrusions 3 c are in close contact with the bottom surface of the recessed portion 5 a of the lower midsole 5. The tip ends of the first protrusions 3 c may be bonded to the bottom surface of the recessed portion 5 a of the lower midsole 5. Alternatively, the upper midsole 3 and the lower midsole 5 may be formed integrally and the tip ends of the first protrusions 3 c may be continuous with the bottom surface of the recessed portion 5 a of the lower midsole 5. By forming the first protrusions 3 c so that their tip ends are bonded to or integral with the lower midsole 5, the shoe having such a sole structure can be prevented from making strange noise by friction between the tip ends of the first protrusions 3 c and the lower midsole 5.

The present disclosure is industrially applicable as a sole structure for, e.g., walking shoes, running shoes, shoes for indoor sports, shoes for ball games that are played on the ground or lawn, etc. 

What is claimed is:
 1. A sole structure for a shoe, comprising: an upper midsole made of an elastic material; and a lower midsole made of an elastic material and bonded from below to the upper midsole, wherein at least one of the upper midsole and the lower midsole has a protrusion protruding toward the other midsole, and when a shoe is in an unworn state, a tip end of the protrusion is not in contact with the other midsole or is in contact with the other midsole such that the tip end of the protrusion can move with respect to the other midsole, and when a foot lands, the tip end of the protrusion is pressed against the other midsole and is thus moved with respect to the other midsole in a direction along a surface of the other midsole.
 2. The sole structure of claim 1, wherein the protrusion is tapered so that its tip end is thinner than its base end.
 3. The sole structure of claim 1, wherein a plurality of the protrusions are formed, and the protrusions adjacent to each other in a longitudinal direction are spaced apart from each other in the longitudinal direction.
 4. The sole structure of claim 1, wherein the protrusion is formed in a region supporting a wearer's heel.
 5. The sole structure of claim 1, wherein a longitudinal dimension of the protrusion is smaller than a lateral dimension thereof.
 6. A sole structure for a shoe, comprising: an upper midsole made of an elastic material; and a lower midsole made of an elastic material and bonded to, or formed integrally with, a lower surface of the upper midsole, wherein at least one of the upper midsole and the lower midsole has a protrusion protruding toward the other midsole, the protrusion has a bent or narrowed intended deformation portion formed in its intermediate portion in a direction in which the protrusion protrudes, and a tip end of the protrusion is in close contact with, is bonded, or is formed integrally with, the other midsole.
 7. The sole structure according to claim 6, wherein the intended deformation portion is bent or narrowed so as to be recessed rearward. 